The present invention relates generally to medical devices, and more specifically to a sternal retractor that minimizes blood loss and fractures of the sternum during use of the sternal retractor.
Approximately 1,000,000 cardiac surgical procedures are performed worldwide each year. In the vast majority (>95%) of these procedures, access to the heart is achieved by dividing the sternum, a procedure known as a sternotomy. The sternum is the “breast bone”, a flat bone approximately 15 to 25 cm in length, 2 to 3 cm in width, and 8 to 16 mm in thickness. In fact, it consists of three bones connected by fused “joints”: the manubrium is 3 to 6 cm long and is located at the cephalad end, the sternum proper is 12 to 15 cm long, while the xiphoid is 1 to 4 cm long and located at the caudal end. The manubrium and sternum are composed of thin (1 to 2 mm) outer and inner tables of cortical bone and a wafer-like, spongiform center of cancellous bone in which the bone marrow resides. Within this bone marrow are numerous venous sinusoids.
Bleeding from the cut sternal edges during a sternotomy can be profuse and prolonged, lasting the duration of the operation, which may be 4 to 8 hours. Cardiac surgical patients are usually given a powerful intravenous anticoagulant, heparin, which prevents the formation of clots during the operation. Total blood loss from the sternal marrow frequently exceeds one liter during a cardiac operation. In conventional operations performed with the use of the heart-lung machine, this shed blood is suctioned up into the venous reservoir of the heart-lung machine and then re-infused into the arterial system of the patient. Fat droplets and other particulate matter is copious within blood shed from bone marrow and these “impurities” are also re-infused into the patient, where they have been implicated as a cause of neurocognitive decline (brain injury), respiratory insufficiency, and renal failure after heart surgery. Recent reports in the literature have advocated discarding this shed blood, yet the sheer volume of blood shed from the sternal bone marrow makes this impractical in most cases. Alternatively, this shed blood may be “washed” in a centrifugal cell scavenge system prior to re-infusing the red blood cell portion. Unfortunately, all other blood components (platelets, coagulation proteins, serum proteins, etc.) are wasted in this system and derangements in the normal clotting ability of the patient often result. In either case, the volume of blood routinely shed from the sternum during cardiac surgery is a major cause of blood transfusion during and after cardiac surgery.
Transfusion associated with cardiac surgery is the single largest civilian demand for blood transfusion worldwide. Within the US, cardiac surgery consumes 10 to 15% of all blood provided by the Red Cross. Thus, there is a clear and immediate need for a way to safely reduce the volume of blood shed from sternal bone marrow during surgical procedures performed via sternotomy.
When the surgeon performs a sternotomy to access the heart or other mediastinal structures, the cut edges of the sternum are typically pried apart with a mechanical device known as a sternal retractor. This device is typically made of stainless steel and includes left and right arms and a rack and pinion mechanism to move the arms apart or together. The arms have blades attached thereto, which actually contact or grip the cut edges of the sternum to apply the opening pressure exerted by the rack and pinion. While these blades are currently available in different shapes and sizes to accommodate the numerous different available retractor systems, none are designed to reduce or prevent bleeding from the edges of the sternum.
Another issue with presently used sternal retractors is the issue of sternal fractures. Presently available blades only contact the central or middle region of the sternal edge. This applies a large amount of pressure against a relatively small surface area of the sternum, which leads to frequent fractures of the sternal edges. These fractures contribute to increased sternal bleeding and are associated with delayed or incomplete healing and increased risk of sternal wound infection.
Accordingly, there is a need for a sternal retractor that reduces bleeding from the cut sternal edge and that reduces fracture of the sternum.